This invention relates to electrical generators and, particularly, relates to wind turbines and superconducting direct current (DC) generators.
A direct drive generator driven by the blades of the wind turbine is efficient and has minimal losses due to transmission of torque from the turbine blades to the DC generator. Direct drive conventional generators on wind turbine towers generally have a power rating of 6 megawatts (MW) or less.
Conventional direct drive generators typically have low torque density and become too heavy for a wind turbine tower at power ratings above about 6 MW. Gearboxes tend to be unreliable and not suitable for long life service in a wind turbine tower.
In addition, alternating current (AC) wind generators must undergo total power conversion to convert the generated power to 50-60 cycle AC at a particular voltage desired by the grid connection. This conversion is typically accomplished by a power electronics (PE) converter consisting of a rectifier in the first stage to convert the AC to direct current (DC) and then an inverter stage to produce the desired AC.
There is a long felt need for direct drive generators for wind turbines capable of generating higher electrical power, e.g., 10 MW. In addition, there is a need for a DC generator which allows the first stage of the converter to be either eliminated or simplified, thereby providing reductions in cost, size and weight, which allow for economical shipping and installation on a wind turbine tower and concomitant reliability increase.